Method for reducing the effects of general anesthetics

ABSTRACT

An apparatus for reversing inhaled anesthesia, which is configured to be positioned along a breathing circuit or anesthesia delivery circuit, includes a filter for removing one or more anesthetic agents from gases passing therethrough, as well as a component for elevating CO 2  levels in gases that are to be inhaled by an individual. The apparatus is configured to be positioned between a Y-connector of the breathing circuit and the portion of the breathing circuit that interfaces with the individual. The CO 2  level-elevating component facilitates an increase in the ventilation of the individual without resulting in a significant decrease in the individual&#39;s P a CO 2  level and, thus, a decrease in the rate at which blood flows through the individual&#39;s brain. A method of reversing the effects of inhaled anesthesia includes increasing the rate of ventilation of an anesthetized individual while causing the individual to inhale gases with elevated amounts of CO 2  and while filtering anesthetic agents from such gases.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/680,469,filed Oct. 7, 2003, pending, which claims the benefit of the filing dateof U.S. Provisional Patent Application Ser. No. 60/466,934, filed May 1,2003, for “Apparatus and Techniques for Reducing the Effects of GeneralAnesthetics,” pending. The disclosure of each of the previouslyreferenced U.S. patent applications and patents is hereby incorporatedby reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to apparatus and techniques forreversing the effects of inhaled general anesthetics. More particularly,the present invention relates to use of ventilation and rebreathingapparatus and, optionally, respiratory monitoring apparatus, inconjunction with one another to reverse the effects of inhaled generalanesthetics.

2. Background of Related Art

General anesthesia is often administered to individuals as surgicalprocedures are being performed. Typically, an individual who is subjectto general anesthesia is “hooked up” to a ventilator by way of abreathing circuit. One or more sensors may communicate with thebreathing circuit to facilitate monitoring of the individual'srespiration, the anesthesia, and, possibly, the individual's blood gasesand blood flow. One or more anesthetic agents are typically administeredto the individual through the breathing circuit.

Examples of breathing circuits that are used while anesthesia is beingadministered to a patient include circular breathing circuits, which arealso referred to in the art as “circle systems,” and Mapleson or Baintype breathing circuits, which are also referred to herein as Bainsystems for the sake of simplicity.

Circle systems are typically used with adult patients. The expiratoryand inspiratory limbs of a breathing circuit of a circle systemcommunicate with one another, with a carbon dioxide remover, such as asoda lime can, being disposed therebetween. As the expiratory andinspiratory limbs communicate with one another, a circle system willtypically include two or more sets of one-way valves to prevent apatient from rebreathing just-expired, CO₂-rich gases.

Bain systems are typically used with smaller patients (e.g., children).Bain systems include linear tubes through which both inspiratory andexpiratory gases flow. Fresh gases are typically directed toward apatient interface to remove the just-expired gases therefrom before thepatient can rebreathe them. As long as the fresh gas flow is higher thanthe flow of the patient's ventilation, there is little or norebreathing.

When a general anesthesia is administered to an individual, respiratoryor inhaled anesthetics are delivered to a patient in low concentrations,typically being diluted to a concentration of about 1% to about 5%,depending on the type of anesthetic agent used. As the individualinhales a general anesthetic agent, the anesthetic agent is carried intothe lungs, where it enters the bloodstream, and is carried by the bloodto various other body tissues. Once the concentration of the anestheticreaches a sufficient level, or threshold level, in the brain, whichdepends upon a variety of individual-specific factors, including thesize and weight of the individual, the individual becomes anesthetized.The individual remains anesthetized so long as the concentration of theanesthetic agent in the brain of the individual remains above thethreshold level.

Once the procedure, typically surgery, for which the general anesthesiais given, has been completed, it is usually desirable to reverse theeffects of the general anesthetic as soon as possible. Reversal of theeffects of general anesthesia allows the surgical team to vacate theoperating room, thereby freeing it up for subsequent surgeries andpossibly reducing the cost of surgery, and also permits the anesthetistto tend to other patients, and conserves the typically expensiveanesthetic agents that are used. In addition, for safety reasons, it isdesirable to minimize the time an individual is under generalanesthesia. Other benefits of quickly reversing anesthesia includebetter cognitive function for elderly patients immediately followingsurgery and enabling patients to protect their own airway sooner.

Reversal or discontinuation of the general anesthetic state requiresthat levels of the anesthetic agent in the brain decrease below thethreshold level, or that the anesthetic agent be removed from theindividual's brain.

It has long been known that activated charcoal and other substances canbe used to selectively adsorb gaseous anesthetic agents. Accordingly,activated charcoal has found conventional use in adsorbers, such as thatdescribed in U.S. Pat. No. 5,471,979, issued to Psaros et al., thatprevents anesthetic agents from escaping the breathing circuit andentering the operating room. In this regard, activated charcoaladsorbers are typically placed in the exhaust flow of the anesthesiadelivery system. The potentially deleterious effects of exhaustanesthetic gases into the operating room are thereby avoided. Further,as most halocarbon anesthetics are considered to be atmosphericpollutants, the charcoals or other adsorbents of conventional anestheticagent adsorbers prevent pollution that may be caused if gaseousanesthetic agents were otherwise released into the environment.

U.S. Pat. No. 5,094,235, issued to Westenskow et al. (hereinafter“Westenskow”) describes the use of activated charcoal to hasten theremoval of gaseous anesthetic agents from breathing circuits. While sucha technique would be useful for preventing the reinhalation ofpreviously exhaled anesthetic agents, more could be done to hasten therate at which anesthetic agents are removed from the individual's brain.

Typically, the rate at which blood flows through the brain and anindividual's breathing rate and breathing volume are the primary factorsthat determine the rate at which the levels of anesthetic agent areremoved from the brain of the individual. The rate of blood flow throughthe brain is a determining factor because the blood carries anestheticagents away from the brain and to the lungs. The breathing rate andbreathing volume are important since they increase the rate at whichanesthetic agent may be removed from the blood and transported out ofthe body through the lungs.

Hyperventilation has been used to increase the breath volume and/or rateof an individual and, thereby, to facilitate the removal of anestheticagents from the individual's lungs. However, hyperventilation typicallyresults in a reduced level of carbon dioxide (CO₂) in blood of theindividual (P_(a)CO₂). When P_(a)CO₂ levels are decreased, the brain isless likely to signal the lungs to breathe on their own and the patientremains dependent on the ventilation from an artificial respirator. SeeU.S. Pat. No. 5,320,093, issued to Raemer (hereinafter “Raemer”).Additionally, the reduced P_(a)CO₂, levels that result fromhyperventilation are known to cause a corresponding reduction in therate at which blood flows through the brain, which actually decreasesthe rate at which the blood can carry anesthetic agents away from thebrain.

Rebreathing processes, in which an individual “rebreathes” previouslyexhaled, CO₂-rich air, have been used to prevent significant decreasesin P_(a)CO₂ levels during such hyperventilation. The apparatus that havebeen conventionally used to effect such processes, however, do notfilter anesthetic agent from the exhaled air before the individualrebreathes the same. Consequently, the patient also rebreathes thepreviously exhaled anesthetic agent, which effectively prolongs theprocess of reversing the general anesthesia.

The computerized system described in Raemer was designed to overcomepurported deficiencies with hyperventilation and rebreathing. The systemof Raemer infuses CO₂ from an external source into the breathing circuitand, thus, into the individual's lungs (i.e., the CO₂ is not rebreathedby the individual) as general anesthesia is being reversed to speed therate of reversal and, thus, recovery of the individual from the generalanesthesia. The teachings of Raemer with respect to infusion of CO₂ froman external source are limited to avoidance of reintroducing anestheticagents into the individual's brain while increasing the individual'sP_(a)CO₂ to a level that will facilitate reinitiation of spontaneousbreathing by his or her brain as early as possible. As the technique andsystem that are taught in Raemer do not include increases in thebreathing rate or breathing volume of an individual, they do notaccelerate the rate at which an individual recovers from anesthesia.

Accordingly, there are needs for processes and apparatus which increasethe rate at which blood carries anesthetic agents from the brain, aswell as the rate at which the lungs expel the anesthetic agents from thebody in order to minimize the time required to reverse the levels ofanesthetic agents in the brain to reverse the effects thereof.

SUMMARY OF THE INVENTION

The present invention includes methods and apparatus for acceleratingthe rate at which an individual recovers from general anesthesia, or forreversing the effects of anesthetic agents. These methods and apparatusmaintain or increase the rate at which blood flows through theindividual's brain, increase the individual's rate of respiration andrespiratory volume, and prevent the individual from reinhalingpreviously exhaled anesthetic agents.

A method according to the present invention includes increasing the rateat which the individual inhales or the volume of gases inhaled by theindividual, which may be effected with a ventilator, or respirator,while causing the individual to at least periodically breathe gasesincluding an elevated fraction of CO₂. This may be effected by causingthe individual to rebreathe at least some of the gases that theindividual has already exhaled or by otherwise increasing the amount ofCO₂ in gases that are to be inhaled by the individual. The rebreathedgases are filtered to at least partially remove some of the previouslyexhaled anesthetic agent or agents therefrom. It is currently preferredthat substantially all anesthetic agents be removed from the exhaledgases prior to rebreathing thereof.

An apparatus that incorporates teachings of the present invention isconfigured to facilitate breathing by an individual at a rapid (i.e.,above-normal) rate, while maintaining CO₂ levels in the individual'sblood, thereby at least maintaining the rate at which blood flows to andthrough the individual's brain. Such an apparatus includes a filter toselectively remove anesthetic agents from gases that have been exhaledby the individual, as well a component that is configured to effectpartial rebreathing by the individual, which is also referred to hereinas a “rebreathing element,” or another component which is configured toincrease the levels of CO₂ inhaled by the individual. The rebreathing orother CO₂ level-elevating component of the apparatus facilitates anincrease in the rate of ventilation of the individual, while CO₂ levelsin blood of the individual (i.e., P_(a)CO₂) remain normal or elevated.The rebreathing or other CO₂ level-elevating component further allowsthe patient to be mechanically ventilated using a respirator at a highvolume or rate while maintaining high or normal levels of CO₂.

Other features and advantages of the present invention will becomeapparent to those of ordinary skill in the art through consideration ofthe ensuing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which illustrate various aspects of exemplaryembodiments of the present invention:

FIG. 1 is a schematic representation of an example of an anesthesiareversal system according to the present invention, including at least aportion of a breathing circuit, an element for increasing aconcentration of carbon dioxide inhaled by a subject that is recoveringfrom anesthesia, and an anesthesia filter and Y-connector positionedalong the breathing circuit;

FIG. 2 schematically depicts an exemplary embodiment of the anesthesiareversal system shown in FIG. 1, which includes a rebreathing tubepositioned along a breathing circuit, between the anesthesia filter andthe Y-connector, which are also positioned along the breathing circuit;

FIG. 3 is a cross-sectional representation of another exemplaryembodiment of the anesthesia reversal system of FIG. 1, in which arebreathing tube which extends from and back to the anesthesia filter;

FIG. 4 is a cross-sectional representation of another embodiment ofanesthesia reversal system of the present invention, in which theanesthesia filter thereof includes an additional deadspace volume whichis configured to effect rebreathing;

FIG. 5 is a cross-sectional representation of still another embodimentof anesthesia reversal system that incorporates teachings of the presentinvention, in which the anesthesia filter includes a volume-adjustabledeadspace to effect rebreathing;

FIGS. 6A and 6B are schematic depictions of yet another embodiment ofanesthesia reversal system of the present invention, in which one ormore conduits and valves are positioned between inspiratory andexpiratory limbs that branch off of the Y-connectors;

FIG. 7 schematically depicts use of an anesthesia reversal systemaccording to the present invention along a conventional circular system;

FIG. 8 schematically illustrates use of an anesthesia reversal system ofthe present invention with a conventional Bain system; and

FIG. 9 is a schematic representation of yet another embodiment ofanesthesia reversal system of the type shown in FIG. 1, in which theelement that increases a concentration of carbon dioxide inhaled by thesubject comprises a carbon dioxide infuser.

DETAILED DESCRIPTION

With reference to the FIG. 1, an anesthesia reversal system 10 accordingto the present invention, which may be positioned along a portion of abreathing circuit 50, between an individual I and a Y-connector 60, andincludes a filter 20 and a rebreathing component 30. An inspiratory limb52 and an expiratory limb 54 may be coupled to Y-connector 60 and, thus,to breathing circuit 50. Notably, the inspiratory and expiratory limbsof some breathing circuits are coaxial. Nonetheless, the junctionbetween the inspiratory and expiratory hoses of such breathing circuitsis still referred to as a “Y-connector.”

As depicted, filter 20 is positioned near the endotracheal tube for anintubated patient or over the mouth and/or nose of an individual I whenbreathing through a mask or mouthpiece so as to remove exhaledanesthetic agents before they flow into the remainder of anesthesiareversal system 10, where they might otherwise be adsorbed by thesurfaces of anesthesia reversal system 10 to remove inhalationanesthetics and be subsequently inhaled by the individual. Of course,placement of filter 20 at alternative locations of anesthesia reversalsystem 10 is also within the scope of the present invention, so long asfilter 20 is positioned between the individual I and rebreathingcomponent 30.

Filter 20 may include a housing 22 with a proximal (relative toindividual I) port 24 and a distal port 26, which, in the depictedexample, are on opposite sides of filter 20. In addition, an anesthesiafilter member 28 is contained within housing 22, in communication withboth proximal port 24 and distal port 26.

Proximal port 24 and distal port 26 may both be configured forconnection to standard breathing circuit fittings. For example, proximalport 24 and distal port 26 may be configured to connect to standard 15mm or 22 mm respiratory fittings. As such, once reversal of generalanesthesia or other inhaled anesthesia is desired, filter 20 may bepositioned along a breathing circuit 50 which is already incommunication with an airway (i.e., the mouth or nose, trachea, andlungs) of individual I.

Anesthesia filter member 28 may comprise any type of filter which isknown to selectively adsorb one or more types of anesthetic agents. Byway of example and not to limit the scope of the present invention,anesthesia filter member 28 may comprise an activated charcoal, oractivated carbon, filter, a crystalline silica molecular sieve, alipid-based absorber (e.g., which operates in accordance with theteachings of U.S. Pat. No. 4,878,388 to Loughlin et al., the disclosureof which is hereby incorporated herein in its entirety by thisreference), a condensation-type filter, or any other type of filteringmechanism which captures or otherwise removes anesthetic vapors from thegases that have been exhaled by individual I. If filter member 28comprises a particulate material, such as activated charcoal orcrystalline silica, the particulate material may be contained by aporous member, a screen, or the like.

As anesthesia filter member 28 communicates with both proximal port 24and distal port 26, it will remove anesthetic agents from gases that areinhaled by individual I, as well as from gases that are exhaled byindividual I.

Optionally, filter 20 may also include an antimicrobial filter member 29of a type known in the art, such as 3M FILTRETE® filter media or otherelectrostatic polypropylene fiber based filter media. Like anesthesiafilter member 28, antimicrobial filter member 29 communicates withbreathing circuit 50 (e.g., by way of proximal port 24 and distal port26 of filter 20). Accordingly, antimicrobial filter member 29 ispositioned to receive substantially all of the gases that are inhaledand exhaled by individual I and, thus, to remove bacteria, viruses, orother pathogens from those gases. Of course, anesthesia reversal systemsthat include antimicrobial filters that are separate from filter 20 arealso within the scope of the present invention.

As shown in FIG. 1, filter 20 and rebreathing component 30 are in directcommunication with one another. As will be shown in greater detailhereinafter, rebreathing component 30 may actually be a part of filter20, rather than separate therefrom.

Rebreathing component 30 may be configured to provide a volume or anamount of deadspace which will maintain a particular level of CO₂ in theblood (i.e., P_(a)CO₂) of individual I. In the depicted example,rebreathing component 30 comprises conduit 31 including a section 32 ofexpandable tubing that can be extended to increase or compressed todecrease the amount of deadspace for containing previously exhaled gaseswhich are to be rebreathed by individual I. Of course, other types ofrebreathing apparatus, such as one of those (excepting the tracheal gasinsufflation device) described in U.S. Pat. No. 6,227,196, issued to Orret al., the disclosure of which is hereby incorporated herein in itsentirety by this reference, or any other known type of partialrebreathing apparatus, may be used in anesthesia reversal system 10 asrebreathing component 30.

It is also within the scope of the present invention to include anotherelement, such as a respiratory flow sensor or gas sampling port 40 atherefor, or a capnometer or gas sampling port 40 b therefor, as knownin the art, at any position along an anesthesia reversal system 10according to the present invention (e.g., close to individual I, betweenfilter 20 and rebreathing component 30, close to Y-connector 60, etc.).For example, when gas sampling ports 40 a, 40 b are used, they may be ofconventional configuration (e.g., for facilitating gas sampling at arate of about 50 ml/min to about 250 ml/min), such as fittings that areconfigured to be disposed at an end or along the length of breathingcircuit 50 or an inspiratory or expiratory limb 52, 54 in communicationtherewith.

Turning now to FIGS. 2 through 6, specific examples of anesthesiareversal systems that incorporate teachings of the present invention areshown.

The embodiment of anesthesia reversal system 10′ shown in FIG. 2includes a rebreathing component 30′ that comprises a section ofrebreathing conduit 31′, which communicates with breathing circuit 50 attwo locations 34′ and 35′ between filter 20 and Y-connector 60.Rebreathing conduit 31′ may include a section 32′ which isvolume-adjustable in a manner known in the art (e.g., by way ofcorrugations, etc.). One or more valves 36′, flow restrictors 37′, or acombination thereof may be positioned along breathing circuit 50 orrebreathing conduit 31′ to control the flow of gases into and out ofconduit 31′.

Another embodiment of anesthesia reversal system 10″, which is shown inFIG. 3, includes a rebreathing component 30″ that communicates directlywith a filter 20″ rather than with breathing circuit 50. As shown,rebreathing component 30″ may be configured as a loop of conduit 31″.One or both ends 38″ and 39″ of conduit 31″ may communicate with filter20″ at a location which is on the distal side of anesthesia filtermember 28 relative to the location of individual I (FIG. 1) (e.g.,between anesthesia filter member 28 and distal port 26) such that gasesare filtered before and/or after passage thereof through conduit 31″.Like rebreathing component 30′ (FIG. 2), rebreathing component 30″ mayinclude a volume-adjustable section 32″.

FIG. 4 depicts another embodiment of anesthesia reversal system 10′″, inwhich filter 20″ figured to provide a deadspace volume 30′″ in which atleast some carbon dioxide rich gases are collected as individual Iexhales. As shown, deadspace volume 30′″ is located on the distal sideof anesthesia filter member 2S, such that the exhaled gases that havecollected therein are filtered as they flow therein and, later, as theyare drawn therefrom (e.g., as individual I (FIG. 1) subsequentlyinhales).

Yet another embodiment of anesthesia reversal system 10″″ thatincorporates teachings of the present invention is pictured in FIG. 5.Anesthesia reversal system 10″″ is much like anesthesia reversal system10′″, which is shown in and described with reference to FIG. 4. Theprimary difference between anesthesia reversal system 10″″ andanesthesia reversal system 10″″ is that the deadspace volume 30″″ ofanesthesia reversal system 10″″, which is at least partially defined bybody 22″″ of filter 20″″, is adjustable, for example, by enlarging orreducing the amount of space occupied by body 22″″ (e.g., by theillustrated sliding motion or as otherwise will be readily apparent tothose of ordinary skill in the art.

As another alternative, pictured in FIGS. 6A and 6B, an anesthesiareversal system 10′″″ of the present invention may include one or moreshunt lines 56′″″ positioned between an inspiratory limb 52′″″ and anexpiratory limb 54′″″ to provide a selectively sized deadspace in thecircuit. In this embodiment, inspiratory limb 52′″″ and expiratory limb54′″″ act as part of the deadspace. A two-way shunt valve 58′″″ ispositioned along each shunt line 56′″″ to selectively direct the flow ofinspired and expired gas.

During normal or baseline breathing, as depicted in FIG. 6A, the two-wayshunt valve 58′″″ will be in a closed position and exhaled gases, whichare represented by the shaded area, will enter the expiratory limb54′″″.

In order to facilitate rebreathing, as pictured in FIG. 6B, two-wayshunt valve 58′″″ is opened, permitting exhaled gases to fill a portionof inspiratory limb 52′″″, substantially all of expiratory limb 54′″″and shunt line 56′″″, all of which serve as deadspace.

The deadspace may be rendered adjustably expandable by using anexpandable conduit for all or part of one or more of inspiratory limb52′″″, expiratory limb 54′″″, and shunt line 56′″″.

Turning now to FIGS. 7 and 8, use of an anesthesia reversal system 10 ofthe present invention in combination with various anesthesia deliverysystems is shown.

In FIG. 7, a circle system 70 is illustrated. Circle system 70, whichincludes an interconnected (e.g., in the configuration of a circle, orloop) inspiratory limb 52′ and expiratory limb 54′. Inspiratory limb 52′and expiratory limb 54′ are coupled to a Y-connector 60 which, in turn,is coupled to a breathing circuit 50′. Breathing circuit 50′ isconfigured to interface with an individual I (FIG. 1) in a known manner(e.g., by intubation, with a mask, with a nasal cannula, etc.). Circlesystem 70 also includes at least two one-way valves 72 and 74, which arepositioned across inspiratory limb 52′ and expiratory limb 54′,respectively, at opposite sides of Y-connector 60. One way valves 72 and74 restrict the flow of gases through circle system 70 to a singledirection, such that expired gases are prevented from flowing directlyinto inspiratory limb 52′ and to prevent individual I from inhalinggases directly from expiratory limb 54′.

Inspiratory limb 52′ of circle system 70 includes at least one gas inlet75, such as a port that facilitates coupling to an anesthesia deliverysystem 300, a mechanical ventilator, or a breathing bag, or whichpermits air from an environment external to circle system 70 (e.g., anoperating room, a patient room in a hospital, etc.) to flow therein. Anexpiratory element 76, such as an expiratory spill valve of a known typeis positioned along expiratory limb 54′ of circle system 70.

As shown, expiratory limb 54′ and expiratory limb 52′ are joined at alocation which is distal relative to Y-connector 60 and individual I bya carbon dioxide removal element 77, such as a soda lime canister. Asone-way valve 72 prevents exhaled gases entering inspiratory limb 52′,the exhaled gases are directed through expiratory limb 54′ and,depending upon the positioning of a bypass valve 78 positioned alongexpiratory limb 54′, possibly into carbon dioxide removal element 77,which reduces the amount of carbon dioxide present in such gases.

Additionally, circle system 70 includes an anesthesia reversal system10. As shown, anesthesia reversal system 10 selectively communicates, byway of bypass valve 78, with expiratory limb 54′ of circle system 70 andis positioned in parallel to carbon dioxide removal element 77. Thevolume of deadspace that may be present within circle system 70 dependsupon whether or not expiratory element 76 causes exhaled gases to remainwithin expiratory limb 54′ and upon whether bypass valve 78 ispositioned to permit exhaled gases to bypass carbon dioxide removalelement 77. In addition, when a mechanical ventilator is coupled to gasinlet 75, the volume of deadspace within circle system 70 depends uponthe proximity of the gas inlet 75 to a junction 80 of anesthesiareversal system 10 with inspiratory limb 52′.

If expiratory element 76 is at least partially closed, depending uponthe positioning of bypass valve 78, at least some of the gases that havebeen exhaled by individual I and which are flowing through expiratorylimb 54′ Nay be diverted from carbon dioxide removal element 77 intoanesthesia reversal system 10. If bypass valve 78 is adjustable to morethan two positions, exhaled gases may be directed into both anesthesiareversal system 10 and carbon dioxide removal element 77. Thus, it maybe possible to carefully regulate the amounts of exhaled gases that aredirected into anesthesia reversal system 10 and carbon dioxide removalelement 77, providing control over the amount of carbon dioxide that isrebreathed by individual I. Further, if bypass valve 78 is positionedsuch that the previously exhaled gases flow through anesthesia reversalsystem 10, the amount of carbon dioxide that remains in gases that passthrough anesthesia reversal system 10 will be relatively high, while theamount of anesthesia present in such gases will be reduced by filter 20.

Then, when individual I inhales or is caused to inhale, at least aportion of the gases that are inhaled (i.e., the gases that remainwithin breathing circuit 50′ and anesthesia reversal system 10) will bepreviously exhaled, CO₂-rich gases.

As circle system 70 may itself serve as a deadspace from which anindividual I may be caused to rebreathe previously exhaled, carbondioxide rich gases, an anesthesia reversal system 10 that is used in acircle system 70 may lack additional deadspace, such as a rebreathingcomponent 30.

Referring now to FIG. 8, a Bain system 90 that incorporates teachings ofthe present invention is depicted. Bain system 90 includes a linearbreathing circuit 50″, a patient interface 92 located at one end 51″ ofbreathing circuit 50″ and a fresh gas inlet 94, which is configured tocommunicate with an anesthesia delivery system 300 of a known type, amechanical ventilator, a breathing bag, or the environment external toBain system 90, positioned along the length of breathing circuit 50″. Inaddition, Bain system 90 includes an anesthesia reversal system 10 thatcommunicates with breathing circuit 50″. Anesthesia reversal system 10is preferably positioned proximate to patient interface 92 so as tooptimize the amount of anesthesia removed from the exhaled gases and,thus, minimize the amount of anesthetic agent rebreathed by anindividual I as the affects of the anesthesia are being reversed.

While FIGS. 2 through 8 illustrate various systems that are useful forproviding a deadspace volume from which an individual I may rebreathe asindividual I is being withdrawn from anesthesia, any other method,apparatus, or system that induces rebreathing of carbon dioxide in amechanical breathing circuit for the purpose of reversing the affects ofanesthesia on an individual are also within the scope of the presentinvention.

Turning now to FIG. 9, an anesthesia reversal system 110 that includes acarbon dioxide infusion element 130 rather than a rebreathing componentis depicted. As illustrated, carbon dioxide infusion element 130communicates with a breathing conduit 150. A filter 120 of anesthesiareversal system 110 is also positioned along breathing conduit 150,proximate to individual I (FIG. 1), so as to reduce the amount ofanesthesia in gases that are exhaled by individual I and, thus, tominimize the amount of anesthesia that remains in any gases that arewithdrawn from breathing conduit 150 and rebreathed by individual I.

With returned reference to FIG. 1 (although anesthesia reversal system110 shown in an described with reference to FIG. 9 may be used in asimilar manner), anesthesia reversal system 10 may be used by placingthe same in communication with a breathing circuit or anesthesiadelivery circuit (e.g., those shown in FIGS. 7 and 8). It is currentlypreferred that filter 20 be positioned proximate to individual I andthat rebreathing component 30 be positioned closer to Y-connector 60. Inthe case of anesthesia recovery system 110 (FIG. 9), the position ofcarbon dioxide infusion element 130 relative to that of filter 120 isirrelevant.

A deadspace (e.g., in the form of the volume within a rebreathingcomponent 30) may be adjusted by an anesthetist to provide the desiredvolume of deadspace therein in order to facilitate rebreathing. Forexample, when the deadspace volume is at least partially located withincorrugated tubing, the deadspace volume may be adjusted by extending orcontracting the length of the corrugated tubing. As another example,when a fixed volume of deadspace is present, or even with avolume-adjustable deadspace, the amount of carbon dioxide within thedeadspace may be tailored by adjusting the flow of “fesh” gases,including recycled gas from which carbon dioxide has been removed. Whenthe flow of “fresh” gases is lower than the flow of individual I'sventilation, rebreathing of gases within the deadspace may occur.

Once anesthesia reversal system 10 has been positioned in communicationwith a breathing circuit or anesthesia delivery system, gases that areexhaled by individual I pass into and through filter 20, which removesat least some anesthetic agents from the exhaled gases. At least aportion of the volume of the filtered, exhaled gases enters and at leasttemporarily remains within the deadspace (e.g., rebreathing component30). Also, by reducing levels of anesthetic agents in gases that areexhaled by individual I, filter 20 may effectively reduce levels ofanesthetic agents that escape into the environment (e.g., the operatingroom, recovery room, atmosphere, etc.) when individual I exhales.

When individual I inhales, at least a portion of the inhaled gases aredrawn from the deadspace (e.g., from rebreathing component 30), with anyother gases being drawn from either the air or from a source ofinspiratory gases that communicate with a ventilator. As the inhaledgases are drawn through breathing circuit 50, they pass through filter20, where at least some of the remaining anesthetic agents therein areremoved therefrom. Notably, in most anesthesia systems, very highconcentrations of oxygen (>90%) are used. Thus, individual I mayrebreathe the same gas many times and still be sufficiently oxygenated.

It is currently preferred that partial rebreathing processes (i.e., onlya portion of the gases inhaled by the patient were previously exhaled,while the other portion of gases are “fresh”) be used in reversing theeffects of inhaled anesthesia. This is because individual I requiressome oxygen during the reversal. Of course, the use of total rebreathingprocesses is also within the scope of the invention. The manner in whichrebreathing is effected may be varied or controlled to provide thedesired affects, while providing individual I with sufficient oxygen.

Of course, a gas sensor and monitor 210 (e.g., an anesthetic gas monitorof a known type) that measures carbon dioxide or oxygen may be used tomonitor the ventilatory gases of individual I. A respiratory flow sensorand monitor 212 may also be used to monitor the flow of ventilation ofindividual I. Gas concentrations may be determined by a processingelement 220 (e.g., a computer processor or controller, a smaller groupof logic circuits, etc.) that communicates with gas sensor and monitor210 and flow sensor and monitor 212, as known in the art. If the carbondioxide or oxygen levels (e.g., blood gas content, respiratory fraction,etc.) reach undesirable levels, adjustments may be made to the deadspacevolume (e.g., within rebreathing component 30), or volume of rebreathedgases, to the concentration of oxygen or carbon dioxide in the otherinhaled gases, or to any combination of the foregoing. Such adjustmentmay be made automatically, such as by processing element 220, which, ofcourse, operates under control of appropriate programming andcommunicates with one or more of a ventilator and valves (e.g., bypassvalve 78 (FIG. 7)) of the anesthesia reversal system 10. Alternatively,adjustment of the deadspace may be effected semiautomatically, such asin accordance with instructions provided by a processing element, ormanually.

By combining a filter 20 and an element for increasing the amount ofcarbon dioxide inhaled by individual I (e.g., with a rebreathingcomponent 30 or carbon dioxide infusion element 130) in an anesthesiareversal apparatus of the present invention, ventilation of anindividual I may be increased while maintaining normal to high P_(a)CO₂levels, which maintains or increases blood flow levels and, thus, therate at which anesthetic agents may be removed from the brain as theincreased ventilation improves the rate at which anesthetic agents areremoved from the blood and, thus, exhaled by individual I.

While much of the description provided herein focuses on the reversal ofgeneral anesthesia, it should be appreciated that the apparatus andmethods of the present invention are useful for reversing the effects ofany type of inhaled anesthesia, whether or not such inhaled anestheticagents have a general anesthetic effect.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some of the presently preferredembodiments. Similarly, other embodiments of the invention may bedevised which do not depart from the spirit or scope of the presentinvention. Features from different embodiments may be employed incombination. The scope of the invention is, therefore, indicated andlimited only by the appended claims and their legal equivalents, ratherthan by the foregoing description. All additions, deletions andmodifications to the invention as disclosed herein which fall within themeaning and scope of the claims are to be embraced thereby.

1. A method employing at least one apparatus for facilitating emergenceof a subject from inhaled anesthesia, the method comprising: decreasinga concentration of anesthetic agents in blood flowing into the brain ofthe subject with at least one apparatus for facilitating emergence of asubject from inhaled anesthesia; increasing blood flow to the brain ofthe subject with the at least one apparatus; and preventing the subjectfrom inhaling previously exhaled anesthetic agents with the at least oneapparatus.
 2. The method of claim 1, wherein increasing blood flow tothe brain comprises: controlling an amount of carbon dioxide inhaled bythe subject.
 3. The method of claim 2, wherein controlling comprisescausing the subject to inhale air or a gas mixture with a fixedconcentration of carbon dioxide.
 4. The method of claim 2, whereincontrolling comprises causing the subject to inhale air or a gas mixturewith an above normal amount of carbon dioxide.
 5. The method of claim 4,wherein controlling comprises causing the subject to rebreathepreviously exhaled gases.
 6. The method of claim 5, wherein causingcomprises adjusting a volume of the previously exhaled gases or anamount of carbon dioxide in the previously exhaled gases.
 7. The methodof claim 6, wherein adjusting comprises permitting a portion of thepreviously exhaled gases to escape a volume from which causing is to beeffected, removing carbon dioxide from a portion of the previouslyexhaled gases, or controlling a flow rate of fresh gases into a volumefrom which causing is to be effected.
 8. The method of claim 5, whereinpreventing comprises removing at least some anesthetic agents from thepreviously exhaled gases.
 9. The method of claim 8, wherein removingcomprises removing substantially all anesthetic agents from thepreviously exhaled gases.
 10. The method of claim 4, wherein causingcomprises causing the subject to inhale air or a gas mixture which issubstantially free of anesthetic agents.
 11. The method of claim 1,further comprising: preventing the subject from inhaling pathogens. 12.A method employing at least one apparatus for facilitating emergence ofa subject from inhaled anesthesia, the method comprising: increasingventilation of the subject relative to the subject's ventilation underanesthesia with a ventilator; causing the subject to inhale gasesincluding an increased amount of carbon dioxide, including at least anatmospheric amount of carbon dioxide, relative to an amount of carbondioxide inhaled by the subject under anesthesia, with a CO₂level-elevating component; and preventing the subject from inhalingpreviously exhaled anesthetic agents with an anesthesia removalcomponent.
 13. The method of claim 12, wherein causing comprisescontrolling an amount of carbon dioxide inhaled by the subject with theCO₂ level-elevating component.
 14. The method of claim 13, whereincontrolling comprises causing the subject to inhale air or a gas mixturewith a fixed concentration of carbon dioxide with the CO₂level-elevating component.
 15. The method of claim 13, whereincontrolling comprises causing the subject to inhale air or a gas mixturewith an above atmospheric amount of carbon dioxide with the CO₂level-elevating component.
 16. The method of claim 15, whereincontrolling comprises causing the subject to rebreathe previouslyexhaled gases with a rebreathing element.
 17. The method of claim 16,wherein causing comprises adjusting a volume of the previously exhaledgases or an amount of carbon dioxide in the previously exhaled gases.18. The method of claim 17, wherein adjusting comprises permitting aportion of the previously exhaled gases to escape a volume of therebreathing element from which causing is to be effected, removingcarbon dioxide from a portion of the previously exhaled gases with aCO₂removal component, or controlling a flow rate of fresh gases into avolume of the rebreathing element from which causing is to be effected.19. The method of claim 16, wherein preventing comprises using theanesthesia removal component to remove at least some anesthetic agentsfrom the previously exhaled gases.
 20. The method of claim 19, whereinremoving comprises using the anesthesia removal component to removesubstantially all anesthetic agents from the previously exhaled gases.21. The method of claim 15, wherein causing the subject to inhale air ora gas mixture with an above normal amount of carbon dioxide comprisesthe subject to inhale air or a gas mixture which is substantially freeof anesthetic agents.
 22. The method of claim 12, further comprising:preventing the subject from inhaling pathogens with a pathogen removalcomponent.